Technical Field
The present invention relates to a method of producing propylene and ethylene from a butene-containing hydrocarbon stream by cracking olefin compounds present in the butene-containing hydrocarbon stream in the presence of a surface modified core-shell ZSM catalyst.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Propylene and ethylene are important compounds in chemical and petrochemical industries. They have been widely used to produce other useful compounds and polymers such as oxo alcohol, propylene oxide, cumene, methyl methacrylate, phenol, acrylic acid, isopropyl alcohol, acrylonitrile, oligomers, polyethylene, polypropylene, etc. A global propylene demand was estimated to be around 90 million tons in 2014, with an average annual growth rate of 4.6%.
The main sources of producing propylene in chemical and petrochemical industries are steam crackers or FCC units, wherein propylene is produced as a byproduct of cracking heavier fractions of a hydrocarbon feedstock. The amount of propylene that is coproduced in a steam cracker greatly depend's on the composition of the hydrocarbon feedstock. However, with the recent decline in oil prices, cracking lighter hydrocarbons is no longer economically advantageous. The reduction of cracking lighter hydrocarbons may result in a reduction of producing propylene and ethylene. On the other hand, thermal cracking (or steam cracking), which is a large source of propylene production in refineries and chemical industries, may form a large amount of methane (a greenhouse gas) as a by-product.
Alternatively, several propylene production processes are also available as means for producing propylene. These processes include methanol-to-olefins (MTO), propane dehydrogenation, catalytic cracking of butenes, and olefins metathesis. Among these, butenes cracking has attracted attentions due to the availability of large and stable supplies of butene from FCC and steam cracking processes. Olefin Cracking Process (UOP-ATOFINA), Propylur (Lurgi), PCC process (ExxonMobil), SUPERFLEX® (Lyondell/Kellogg), and Mobil's Olefin Inter conversion Process (MOI) are examples of commercially available production processes for producing lower olefins such as ethylene and propylene via hydrocarbon streams containing C4-C5.
Modified zeolite catalyst has been studied for cracking reactions of butene to propylene and ethylene. For example, Rongrong Zhang et al. (Chinese Journal of Chemical Engineering, 2015, v.23, pp. 1131-1137) prepared a silver modified HZSM-5 zeolite catalyst via ion exchange method, and further used the catalyst towards catalytic cracking of 1-butene. The maximum propylene yield was about 30% by mass and the activity of the silver modified HZSM-5. zeolite catalyst was found to be higher when compared to the parent zeolite. Furthermore, Jianwen Li et al. (Fuel Processing Technology 2015, v. pp. 32-38) reported that a HZSM-5 zeolite catalyst, which has been modified by phosphorus and/or iron, enhanced selectivity of the cracking reactions towards propylene formation. However, a gradual deactivation of the catalyst was observed in the phosphorus and/or iron modified catalyst. Accordingly, the butene conversion was dropped by about 20%, in the first 25 hours of butene cracking. In another study, Higuchi et al. (U.S. Pat. No. 9,205,415 B2) disclosed a process for propylene production using MFI or MEL-type catalyst having Si/Al atomic ratio of 500 to 1000. Effect of loading different alkali metal compound such as K, Na and Li were tested using dimethyl ether as feed. A propylene yield of about 27% by mole was observed when 1-butene was used as a feed. Moreover, Midorikawa et al. (U.S. Pat. No. 9,192,922) disclosed propylene production using ZSM-5 type catalyst modified with silica and phosphorous. The reaction was carried out in fluidized bed reactor with a feed having an ethylene to 1-butene weight ratio of 80:20. It was shown that after 3 hours of the reaction, the ethylene conversion was about 63.3% and the propylene yield was about 21.2%. In addition, Van Westrenen et al. (U.S. Pat. No. 8,822,749B2) disclosed mixed catalyst system having MFI (ZSM-5) and TON (ZSM-22) or MFI (ZSM-5) and MTT (ZSM-23) type molecular sieves for propylene production using dimethyl ether and 1-butene as a feed. Mixed catalyst system slightly enhances the propylene production when compared to single catalyst system. Besides, Al-Khattaf et al. (US Patent Application No. 2016/0130197 A1) disclosed a process for cracking C4 olefins to propylene and ethylene via an MFI zeolite catalyst having a Si/Al molar ratio of 2000. It was shown that acid-treating or base-treating the catalyst increases the propylene production yield. The increased propylene yield after base-treating the catalyst may be due to an enrichment of silanol group in the catalyst. Knowing the above disclosure, however, there appear to be no report on utilizing a surface modified ZSM-5 as a cracking catalyst for the production of light olefins such as ethylene and propylene from a feed containing butene.
In view of the forgoing, one objective of the present invention is to provide a method of producing propylene and ethylene from a butene-containing hydrocarbon stream by cracking olefin compounds in the butene-containing hydrocarbon stream in the presence of a surface modified core-shell ZSM catalyst Further embodiments of the present invention relates to methods of making the core-shell ZSM catalyst.